Generally, an optical disk player records a signal on a disk in digital form and reproduces the signal according to received light intensity by first projecting a high-intensity light such as a laser beam onto the surface of the disk and then detecting the reflected light.
Conventionally, in a system for single-sided playback only, as shown in FIG. 1, a digital video signal and audio signal are picked up from a disk 5 by a pickup 10 and are demodulated in a demodulator 20. Thereafter, from among the received digital signals (video and audio) from demodulator 20, a charge-coupled device (CCD) 30 outputs only the video signal as an electric signal. Subsequently, a synchronizing signal detector 40 detects the horizontal and vertical synchronizing signals from the video output of CCD 30 and an H sync separator 50 detects only the horizontal sync signal. A first phase comparator 60 then detects the phase difference between the horizontal synchronizing signal (e.g., 15.75 KHz) separated by H sync separator 50 and an input reference horizontal synchronizing signal, so as to output a signal corresponding to the detected phase difference. A color burst signal separator 70 detects the color burst signal (e.g., 3.58 MHz for NTSC) from the video signal output of CCD 30. It will be noted that a second phase comparator 80 detects the phase difference of the color burst signal from color burst signal separator 70 and a reference color burst signal.
An adder 90 adds the phase differences output from the first and second phase comparators 60 and 80, and an amplifier 100 amplifies the summed phase differences to output the result to a spindle motor driver 120. Spindle motor driver 120 converts the phase difference signal output from amplifier 100 into a pulse-width-modulated (PWM) signal so as to drive spindle motor 130.
Meanwhile, a voltage-controlled oscillator (VCO) 110 converts the summed phase difference signal from amplifier 100 into an oscillating frequency which is output to a read clock control port of CCD 30.
However, since an optical disk player for single-sided playback is stabilized by chucking the disk in only one direction (i.e., from the bottom surface) by a clamp installed on a turntable for rotating the optical disk, so as to be raised and lowered and be rotatable as shown in FIG. 2, a double-sided disk cannot be reproduced. Thus, when the disk is reproduced from the top (opposite surface), the spindle control amount increases even though such an optical disk player is mechanically modified so as to be capable of reproducing the double-sided disk.
In the case of a conventional single-sided laser disk, as shown in FIG. 3, since the inner diameter of the hole has an eccentricity of 55 mm+100 .mu.m. However, since chucking stabilization is performed with respect to the single-sided disk in the table structure, the eccentricity amount can be decreased.
For a double-sided disk, since the holes of the top and bottom surfaces of the disk have inner diameters a and b, respectively, as shown in FIG. 4, the inconsistencies with respect to the hole center are produced in manufacturing the disk. In other words, because of the instability induced in the spindle servo due to the difference of the hole centers of the top surface and bottom surface of the disk, when the disk shown in FIG. 4 is reproduced, the pictures become unstable.
To overcome this problem, a structure has been proposed which provides for dual chucking of the disk. The system is first chucked during the bottom-surface playback, and chucked again during the top-surface playback. However, a dual chucking mechanism is complicated and expensive. Such an apparatus for compensating for the eccentricity amount by matching the gains of the tracking servo and tracking position servo in a single-sided disk is disclosed in U.S. Pat. No. 5,121,374.